Takuro Fujikawa

Column percolation test for contaminated soils: Key factors for standardization

Column percolation tests may be suitable for prediction of chemical leaching from soil and soil materials. However, compared with batch leaching tests, they are time-consuming. It is therefore important to investigate ways to shorten the tests without affecting the quality of results. In this study, we evaluate the feasibility of decreasing testing time by increasing flow rate and decreasing equilibration time compared to the conditions specified in ISO/TS 21268-3, with equilibration periods of 48h and flow rate of 12mL/h. We tested three equilibration periods (0, 12-16, and 48h) and two flow rates (12 and 36mL/h) on four different soils and compared the inorganic constituent releases. For soils A and D, we observed similar values for all conditions except for the 0h-36mL/h case. For soil B, we observed no appreciable differences between the tested conditions, while for soil C there were no consistent trends probably due to the difference in ongoing oxidation reactions between soil samples. These results suggest that column percolation tests can be shortened from 20 to 30days to 7-9days by decreasing the equilibration time to 12-16h and increasing the flow rate to 36mL/h for inorganic substances.

Reproducibility of up-flow column percolation tests for contaminated soils

Up-flow column percolation tests are used at laboratory scale to assess the leaching behavior of hazardous substance from contaminated soils in a specific condition as a function of time. Monitoring the quality of these test results inter or within laboratory is crucial, especially if used for Environment-related legal policy or for routine testing purposes. We tested three different sandy loam type soils (Soils I, II and III) to determine the reproducibility (variability inter laboratory) of test results and to evaluate the difference in the test results within laboratory. Up-flow column percolation tests were performed following the procedure described in the ISO/TS 21268–3. This procedure consists of percolating solution (calcium chloride 1 mM) from bottom to top at a flow rate of 12 mL/h through softly compacted soil contained in a column of 5 cm diameter and 30 ± 5 cm height. Eluate samples were collected at liquid-to-solid ratio of 0.1, 0.2, 0.5, 1, 2, 5 and 10 L/kg and analyzed for quantification of the target elements (Cu, As, Se, Cl, Ca, F, Mg, DOC and B in this research). For Soil I, 17 institutions in Japan joined this validation test. The up-flow column experiments were conducted in duplicate, after 48 h of equilibration time and at a flow rate of 12 mL/h. Column percolation test results from Soils II and III were used to evaluate the difference in test results from the experiments conducted in duplicate in a single laboratory, after 16 h of equilibration time and at a flow rate of 36 mL/h. Overall results showed good reproducibility (expressed in terms of the coefficient of variation, CV, calculated by dividing the standard deviation by the mean), as the CV was lower than 30% in more than 90% of the test results associated with Soil I. Moreover, low variability (expressed in terms of difference between the two test results divided by the mean) was observed in the test results related to Soils II and III, with a variability lower than 30% in more than 88% of the cases for Soil II and in more than 96% of the cases for Soil III. We also discussed the possible factors that affect the reproducibility and variability in the test results from the up-flow column percolation tests. The low variability inter and within laboratory obtained in this research indicates that the ISO/TS 21268–3 can be successfully upgraded to a fully validated ISO standard.

Evaluation of Environmental Safety on Municipal Solid Waste Incineration Bottom Ash Using Aging Method

Since Japan does not have enough space for landfilling, the use of incineration bottom ash (IBA) from municipal solid waste (MSW) as a construction material is being explored. However IBA contains significant toxic materials, and it has to be immobilized before it can be used as a ground geo-material. This study examines aging methods to immobilize IBA by natural rain and carbon dioxide in the air at landfill sites. This paper reports the leaching properties of IBA from MSW in order to evaluate the environmental safety by means of Japanese leaching test No. 46 (Notifications No. 46 by Japanese Ministry of the Environment (JLT 46)), up-flow percolation column test, and pH-dependent test. The leaching concentrations of heavy metals from IBA were found to be influenced by the aging process. It was revealed that the concentration of lead (Pb), hexavalent chromium (Cr (VI)), cadmium (Cd) and boron (B) meet the environmental quality standard values for ground material. Also it was revealed that the possibility of leaching in the long term is low.

Application of Soil Improvement Material Using Recycled Gypsum Considering the Environmental Safety

Currently, in Japan, recycling of various industrial waste is proceeding to create a recycling-oriented society. Waste gypsum boards generated at the time of constructing and dismantling buildings are industrial waste requiring recycling. Waste gypsum boards are separated into board paper and recycled gypsum in the intermediate processing facilities. The recycled gypsum powder is effectively used as a raw material for cement, raw material for neutral ground improvement materials, and ground improvement materials for agriculture. However, when used as a ground improvement material, it is pointed out that the fluorine contained in recycled gypsum powder may dissolve into the improved ground. Therefore, to use recycled gypsum powder effectively on the ground, it is important to ensure that the fluorine is insolubilized for the environmental safety. In this research, applicability of ground improvement solidification material using regenerated hemihydrate gypsum powder was investigated. Especially on improvement of soft ground, the results of investigation is reported focusing on the improved properties of regenerated hemihydrate gypsum improved soil, long term durability, and re-sludge characteristics.

Mechanical Characteristics of Incineration Bottom Ash from Disaster Waste Caused by the Great East Japan Earthquake

The Great East Japan Earthquake resulted in extensive damage and left a vast amount of debris. The debris from the disaster has been incinerated to reduce the volume. This study focused on the predicted future demand of land soil, for example, to use in post-disaster reconstruction works. In order to examine the availability to recycle and utilize the incineration bottom ash from the disaster debris, the material properties of the incineration bottom ash was evaluated by soil experiments. Features of incineration bottom ash recycled material were compared with general incineration bottom ash from F City. A modified CBR test (JIS A 1211) was adapted to evaluate the availability of using the material as subgrade and roadbed material. A constant pressure direct shear test was employed to assess the shear properties. The results show that the incineration bottom ash recycled material has equivalent shear properties with regard to physical composition compared to general incineration bottom ash. The study reports that there is a possibility for incineration bottom ash recycled material to be effectively utilized as a roadbed material and used as a soil material with varied strengths.

APPLICABILITY TO ASPHALT MIXTURE FILLER MATERIALS OF THE REPRODUCTION GYPSUM

This study deals with recycling of gypsum as well as recycling of hemihydrate gypsum generated from burning of waste plasterboards. Correspondingly, this study is devoted to examine the effect of gypsum content and the surrounding environment on the mechanical characteristics of asphalt mixtures and to evaluate the validity of using the resulting asphalt mixtures as a paving materials. Therefore, the main purpose of this study is to find the recommended gypsum rates to be used within the asphalt mixtures. As for the substitute rate for filler materials, around 40%, around 75% of reproduction and hemihydrate gypsum substitutes are possible with reproduction a type of radical gypsum with the dense particle size asphalt mixture.And, it became clear in the porous asphalt mixture that a 100% substitute was possible.Also, it has been found that no heavy metal has been detected during tank leaching testing of an asphalt mixture incorporate gypsum. 本研究では，廃石膏ボードを紙片類と破砕分離した再生二水石膏と，さらに再生二水石膏を焼成処理することによって得られる再生半水石膏に着目し，これらの再生石膏をアスファルト混合物フィラー材に代替するリサイクル方法の検討を行った．その結果，再生石膏をアスファルト混合物に混合すると，空隙率の増加，耐水性の低下がみられる一方，残留安定度の増加がみられた．フィラー材に対しての代替率は，密粒度アスファルト混合物では再生二水石膏で40%程度，再生半水石膏75%程度，ポーラスアスファルト混合物においては100%代替が可能であることが明らかとなった．また，周辺環境へ及ぼす影響について，タンクリーチング試験から検討した結果，今回のアスファルト混合物からの重金属等の溶出はみられないことが示された．

MECHANICAL PROPERTIES OF PAVING MATERIAL OF PEDESTRIANS-FRIENDLY PAVEMENTS USING COAL FLY ASH

Materials for paving on the pedestrians-friendly pavements, which are constructed as the pavements and the promenade in parks, attracts attention, because it is welcomed as eco friendly method considered recent global warming. On the other hand, under the recent influence of rising crude oil price, the demand of thermal power generated by coal has been growing, causing a large amount of coal fly ash. However as securing the large scale of disposal site has been getting more difficult, widening effective utilization of coal ash has become a fairly critical theme. Considering those conditions, this study concludes the properties of the strength of materials using two types of coal ash, PFBC and FA. And then we tried to improve the vulnerability by adding the wasted bamboo crashed to the chip state as a step against the crack. The main conclusions are summarized as follows: 1) Materials added PFBC ash has prominent congealment effect, compared with material added FA ash. 2) In case of using of FA ash, it is possible for the material to gain the higher strength than the PFBCs at the same level, by mixing cement. 3) Destruction due to vulnerability is restrained by mixing 10 percent bamboo chips.